Composite structure having a non-planar interface and method of making same

ABSTRACT

A composite structure includes a first portion comprising a first metallic material, a monolayer of particles extending into and bonded with the first portion, and a second portion comprising a second material, the second portion bonded with the monolayer of particles and extending into interstices between the particles. A method for fabricating a composite structure includes bonding a monolayer of particles to a first portion comprising a first metallic material, such that the monolayer of particles extends into the first portion and bonding a second portion comprising a second material to the monolayer of particles, such that the second portion extends into interstices between the particles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a composite structure including a non-planarinterface and a method of making the composite structure.

2. Description of the Related Art

Metallic structures often comprise two or more joined materials thathave different properties and characteristics. Often such disparatematerials are joined together into one component because portions of thecomponent are subjected to different environments. For example, the bodyof a drilling bit, such as those used in oilfield operations, issubjected to high torsion loads during drilling, while the cuttingsurfaces thereof encounter very hard, abrasive materials. Accordingly,rock drilling bit bodies are generally made of steel, while the cuttingsurfaces often comprise tungsten carbide or polycrystalline diamondcomposites. Steel provides the material properties required to endurehigh torsion loads, while tungsten carbide or polycrystalline diamondprovides deformation- and wear-resistant material properties. Similarconfigurations are also found in mining bits and roadbed milling bitsused to break apart old roadbeds.

When such disparate materials are joined together, the mechanicalresponse of the resulting union is affected by the differences inelastic, plastic, and/or thermal expansion properties that causeinternal residual stresses to develop within the union, and that causeconcentration of applied stress at the interface, enabling prematurefailure of the union in service. FIG. 1 illustrates two disparatematerial portions 102, 104 joined along an interface 106, which may beplanar or non-planar. Such components are often formed using powdermetallurgy techniques. For example, the material portion 102 mayinitially comprise a mixture of steel and tungsten carbide powders andthe material portion 104 may comprise a steel powder. The portions 102,104 may then be cold isostatically pressed to achieve sufficientdensification providing handling strength and then either hot forged orhot isostatically pressed to achieve full density. Alternatively, theportion 102 may initially comprise a sintered cemented carbide and thematerial portion 104 may initially comprise a mixture of diamond andmetals powders. The portions 102, 104 may then be hot pressed at veryhigh pressure to achieve full density.

In both cases, densification involves the heating of the portions 102,104 in contact with one another under high pressure such that adjacentparticles within the portions 102, 104 are plastically deformed andsolid state diffusion bonded, or partially melted and resolidified.

Such structures exhibit a mechanical discontinuity along an interface106 of the disparate materials. The effects of this discontinuity onmechanical response of the union typically limit the useful strength ofthese structures. For example, if the portion 102 has a coefficient ofthermal expansion (CTE) that is significantly lower than that of theportion 104, merely cooling the joined materials from the finaldensification temperature may generate sufficient stress at theinterface 106 to disbond/disjoin the portions 102, 104. Even if thermalresidual stress in the joined portions 102, 104 were below the failurethreshold, the application of external loading on the joined portions102, 104 would result in a concentration of stress at the interface dueto elastic modulus and plastic yielding differences between the portion102, 104. The superposition of thermal residual stress and concentratedload stress may disbond/disjoin the portions 102, 104.

Various techniques are known to the art for improving the stressdistributions along such disparate material interfaces (e.g., theinterface 106) and, thus, improving the useful strength of thesestructures. For example, one technique is to roughen the interfacesurface 106 between the disparate materials 102, 104 before joining.Adding topographic complexity in a dimension normal to the interfacesurface creates a zone of material that behaves as though its propertiesare intermediate the two joined disparate materials. This configurationis often referred to as a “non-planar interface”, whether the interfaceis broadly planar or curved. In one example, illustrated in FIG. 2A, aninterface surface 202 of the portion 104 is roughened prior to joiningthe portion 102 thereto. Alternatively, as shown in FIG. 2B, localizedareas of an interface surface 204 of the portion 104 are melted, forexample, with an electron beam, laser, or other intense, localizedheating source prior to joining the portion 102 thereto.

In either case, when the portion 102 is joined to the portion 104, thematerial comprising the portion 102 fills the recesses in the roughenedsurfaces 202, 204 to further retain the portions 102, 104 together.While the techniques described in relation to FIGS. 2A-2B may beeffective in improving the strength of the bond or joint between theportions 102, 104, they each require additional processing to preparethe interface surfaces 202, 204 for joining. The additional processingmay, in some instances, also be costly. For example, the electron beam,laser, or other localized, intense heat source equipment used to meltareas of the interface surface 204 may be very expensive to purchase,maintain, and operate.

Other techniques that have been used to aid in retaining disparatematerial portions together include machining retention features in oneof the portions and urging material of the other portion into thefeatures. FIGS. 3A-3C illustrates one particular example of such atechnique. A plurality of radial grooves 302 (only one labeled forclarity) and a circumferential groove 303 are machined into a face 304of a cutting blank 306 comprising, for example, steel. A cutting portion308, comprising a second material, e.g., tungsten carbide,polycrystalline diamond, etc., is formed onto the face 304, such thatthe cutting portion 308 extends into the grooves 302, 303. Thenon-planar interface between the cutting blank 306 and the cuttingportion 308 aids in retaining the cutting portion 308 on the cuttingblank 306, as compared to an interface that omits the grooves 302, 303.Some designs have further included undercut grooves, such as illustratedin FIG. 3C, to further enhance retention of the cutting portion 308 onthe cutting blank 306.

While such techniques often are successful in retaining disparatematerials together, the additional machining steps required to form thegrooves 302, 303 may add substantial cost and complexity to the finishedproduct. The preferred die-pressing method for creating irregular orgrooved surfaces via powder fabrication is restricted to geometries thatprovide positive draft to allow die withdrawal. Further, it may bedifficult to fully fill the grooves 302, 303, with the second material,especially if they are narrow or undercut (as illustrated in FIG. 3C).

As illustrated in FIG. 4, designs have also included protrusions 402(only one labeled for clarity) extending from a first material portion404 and into a second material portion 406, forming a non-planarinterface 408.

Yet another technique used to mitigate stress concentrations along suchdisparate material interfaces is to employ a “functional gradientdesign,” as shown in FIG. 5, wherein a third material 502 is disposed inthe interface 106 between the two disparate materials 102, 104. Thethird material 502 has properties that are generally between those ofthe disparate materials 102 and 104. In other words, the third orgradient material 502 may have, for example, elastic plastic, thermalexpansion properties intermediate between those of the first disparatematerial 102 those of the second disparate material 104. Multiple suchintermediate layers or single graduated layer may be employed to furtherreduce the magnitude(s) of disparities of the included interfaces. Whilesuch structures address the property compatibility issues describedabove, their complexity often adds prohibitive fabrication cost and maybe incompatible with preferred fabrication methods.

The present invention is directed to overcoming, or at least reducing,the effects of one or more of the problems set forth above.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a composite structure isprovided. The composite structure includes a first portion comprising afirst metallic material, a monolayer of particles extending into andbonded with the first portion, and a second portion comprising a secondmaterial, the second portion bonded with the monolayer of particles andextending into interstices between the particles.

In another aspect of the present invention, an insert for a rock bit isprovided. The insert includes a substrate comprising a first metallicmaterial, a plurality of particles bonded with the substrate, and adensified portion comprising a second material, the densified portionbonded with the plurality of particles and extending into intersticesbetween the particles.

In yet another aspect of the present invention, a composite pick isprovided. The pick includes a tip comprising a first metallic material,a plurality of particles bonded with the tip, and a densified portioncomprising a second material, the densified portion bonded with theplurality of particles and extending into interstices between theparticles.

In another aspect of the present invention, a method for fabricating acomposite structure is provided. The method includes bonding a monolayerof particles to a first portion comprising a first metallic material,such that the monolayer of particles extends into the first portion andbonding a second portion comprising a second material to the monolayerof particles, such that the second portion extends into intersticesbetween the particles.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich the leftmost significant digit(s) in the reference numeralsdenote(s) the first figure in which the respective reference numeralsappear.

FIG. 1 is a stylized, cross-sectional side view of a first conventionalcomposite structure of the prior art.

FIGS. 2A-2B are stylized, enlarged alternative views of a portion of thecomposite structure of prior art FIG. 1.

FIG. 3A is a top view of a conventional composite cutter of the priorart.

FIG. 3B is a cross-sectional view of the conventional composite cutterof the prior art taken along the line 3B-3B in FIG. 3A.

FIG. 3C is a cross-sectional view of the conventional composite cutterof the prior art taken along the line 3C-3C in FIG. 3A.

FIG. 4 is a stylized, cross-sectional side view of a second conventionalcomposite structure of the prior art.

FIG. 5 is a stylized, cross-sectional side view of a third conventionalcomposite structure of the prior art.

FIG. 6 is a stylized, cross-sectional side view of a first illustrativeembodiment of a composite structure having a non-planar interfaceaccording to the present invention.

FIG. 7 is a stylized, cross-sectional, enlarged portion of oneillustrative embodiment of the composite structure of FIG. 6illustrating neck bonds.

FIG. 8 is a stylized, cross-sectional side view of an intermediate stageduring fabrication of the composite structure of FIG. 6.

FIG. 9 is a stylized, cross-sectional side view illustrating fillingfine powder around the particles of the composite structure intermediatestage of FIG. 8.

FIG. 10 is a stylized, cross-sectional side view illustrating densifyingthe powder of FIG. 9.

FIG. 11 is a stylized, cross-sectional side view illustrating infusingmolten metal around the particles of the composite structureintermediate stage of FIG. 8.

FIG. 12 is a stylized, cross-sectional, enlarged portion of oneillustrative embodiment of the composite structure of FIG. 6.

FIG. 13 is a stylized, cross-sectional side view illustrating variousparticulate shape embodiments according to the present invention.

FIG. 14 is a stylized, cross-sectional side view of a secondillustrative embodiment of a composite structure according to thepresent invention.

FIG. 15 is a perspective view of an exemplary roller-cone rock bitincluding inserts or cutters according to the present invention.

FIG. 16 is a side view of an exemplary fixed cutter rock bit includinginserts or cutters according to the present invention.

FIG. 17 is a perspective view of an illustrative embodiment of anintermediate stage of a rock bit insert according to the presentinvention.

FIG. 18 is a top view of a first alternative embodiment of anintermediate stage of a rock bit insert according to the presentinvention.

FIG. 19 is a top view of a second alternative embodiment of anintermediate stage of a rock bit insert according to the presentinvention.

FIG. 20 is a perspective view of an illustrative embodiment of a road ormining pick tip according to the present invention.

FIG. 21 is a depiction of the macrostructure of one particularembodiment of a road or mining pick according to the present invention.

FIG. 22 is a depiction of a portion of the microstructure of the road ormining pick of FIG. 21.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedeveloper's specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The present invention relates to a structure comprising disparatematerials joined along a non-planar interface that exhibits, in oneillustrative embodiment, an interlocking geometry and a method forfabricating the structure. While it is not so limited, the structure ofthe present invention is particularly applicable to cemented carbidecomposites and their incorporation in layered, functionally gradedstructures with disparate cemented carbides, diamond composites, metals,or metal alloys. The non-planar interface of the present inventionallows fabrication of powder preforms incorporating fully dense elementsby direct pressing or cold isostatic pressing, and powder forging ofsuch preforms. In particular, the present invention mitigates or avoidsthe problem of decompression cracking between fully dense and powderregions during the unload portion of an isostatic pressing cycle.

FIG. 6 depicts one illustrative embodiment of a composite structure 600incorporating a non-planar interface according to the present invention.In this embodiment, the structure 600 comprises a monolayer of particles605 (only one labeled for clarity) formed integrally with a metallicsubstrate material 610. The particles 605 define an open framework thatis substantially filled with a second material 615. The particles 605may comprise the same material as the substrate 610, a chemical ormetallurgical variant of the substrate 610, a metal or a metal alloy. Inone embodiment, shown in FIG. 7, the substrate 610 comprises a sinteredpowder and the particles 605 are co-sintered with the substrate 610. Inthis embodiment, the particles 605 are attached to the substrate 610and, in some cases to each other, primarily by metallurgical neck bonds705 grown during sintering. In some embodiments, the particles 605extend into the substrate 610. Mechanisms that are operative during neckbond growth include: viscous flow, plastic flow,evaporation-condensation, volume diffusion, grain boundary diffusion,and surface diffusion. The particles 605 may be attached to thesubstrate 610 by various processes producing metallurgical bonding, suchas liquid phase sintering, solid-state sintering or diffusion bonding,welding, and brazing. FIG. 8 illustrates an intermediate configuration,prior to adding the second material 615 to the composite structure 600.

The second material 615 may be formed by substantially filling the openvolume between the particles 605 with a fine metallic powder 905, asshown in FIG. 9, then pressure densifying the second material 615 (e.g.,the fine powder 905), as shown in FIG. 10. Alternatively, the secondmaterial 615 may be formed by infiltrating the open volume between theparticles 605 with liquid metal and solidifying the metal 1105 asillustrated in FIG. 11, to form the second material 615 (of FIG. 6).Thus, the second material 615, whether formed using powder or liquidmetal techniques, comprises a densified portion. Note, as depicted inFIG. 12, that the particles 605 extend from the substrate 610 such thatthe particles 605 and the substrate 610 define recesses 1205. Therecesses 1205 exhibit negative draft angles (e.g., the negative draftangle 1210) or are “undercut.” Generally, a draft angle of 90 degrees isneutral. Thus, a draft angle of less than 90 degrees (as illustrated inFIG. 12) is a negative draft angle. Draft angles that are greater than90 degrees are considered positive draft angles. While the presentinvention is not so limited, in particular embodiments, the draft anglemay be within a range of about 3 degrees to about 85 degrees.

The second material 615 extends into the recesses 1205, which providesmechanical locking of the second material 615 to the particles 605.Moreover, the particles 605 provide a tortuous bonding surface havingsubstantially more bonding area for both the substrate 610 and thesecond material 615 as compared to a planar interface. These factorscontribute to improved mechanical interlocking strength duringintermediate processing steps and increased interfacial strength in thefinished structure.

While the particles 605 are illustrated in FIG. 6 as being substantiallyspherical, the present invention is not so limited. Rather, theparticles 605 may take on many other shapes, such as oblate spheroids1305, cylinders 1310, and irregular shapes 1315, as illustrated in FIG.13, including, for example, acicular, fibrous, flaky, granular,dendritic, and blocky shapes. Further, the particles 605 may, in someembodiments, be arranged in a particular pattern or they may be randomlydispersed on the substrate material 610.

Note that substrate 610 may comprise either the “soft” or “hard” portionof the composite structure 600. For example, wherein the substrate 610comprises a cemented carbide and the second material 615 comprises apolycrystalline diamond material, the cemented carbide substrate 610represents the “soft” portion of the composite structure 600. Asillustrated in FIG. 14, the composite structure 600, for example, may beincorporated into a yet larger composite structure 1400 including asecond monolayer of particles 1405 (only one labeled for clarity) and athird material 1410 that is softer than the substrate 610. In such aconfiguration, the substrate 610 corresponds to the “hard” portion ofthe composite couple of the substrate 610 and the third material 1410.

Particular implementations of the present invention depend on many scaleand property aspects of the components and component materials. Forexample, in the case of polycrystalline diamond composite cutters orinsert elements, the desirable thickness of the particle layer (e.g.,the layers of particles 605, 1405) depends upon the polycrystallinediamond layer thickness and the shape of the substrate surface. Forplanar or simply curved surfaces, a particle size corresponding to about80% of the polycrystalline diamond layer thickness may be used. Dimpled,ribbed, or faceted substrate surfaces may require smaller averageparticle sizes or a wider size distribution for conformation to thesubstrate surface. Multiple sizes or shapes of particles maybe used toenhance particle coverage and effective non-planar interface zone width.

The non-planar interface structure of the present invention may beimplemented in various products, such as a roller-cone rock bit 1500,shown in FIG. 15, or a fixed cutter rock bit 1600, shown in FIG. 16. Therock bits 1500, 1600 comprises a plurality of polycrystalline diamondcoated inserts 1505, 1605, respectively, (only one labeled in eachfigure for clarity) that ablate rock formations during oilfield drillingoperations. FIG. 17 illustrates one particular embodiment of such aninsert 1705 at an intermediate stage of fabrication. The insert 1705comprises a plurality of tungsten carbide/cobalt spherical pellets 1710sintered onto a cemented carbide substrate 1715 of the same composition.In the illustrated example, the pellets 1710 have sizes corresponding toa 16/20 mesh. In other embodiments, the pellets 1710 have sizescorresponding to 80/200 mesh, 40/60 mesh, and 20/30 mesh but maycomprise other sizes depending upon the particular implementation.

As noted above, the particles or pellets may take on various shapes. Forexample, FIGS. 18-19 illustrate an exemplary insert comprisingrod-shaped or cylindrical tungsten carbide/cobalt particles 1805sintered onto a substrate 1810 of the same material. In FIG. 18, theparticles 1805 are arranged in a spiral fashion, while they are arrangedrandomly in FIG. 19. Irrespective of the particle shape and arrangement,the interstices between the particles or pellets 1710, 1805 are filledwith diamond-containing particle mixes, held in place by a formed canthat defines the final external shape. The assembly is subsequentlydensified at high temperature and pressure, achieving full density ofthe composite structure.

Another exemplary implementation of the non-planar interface structureof the present invention is that of a composite road pick used formilling roadbeds prior to resurfacing. Such picks are also used inearth-boring equipment for mining applications. FIG. 20 depicts asintered, cemented carbide tip 2005 with an integral particulatenon-planar interface layer 2010 disposed on an undulant surface 2015. Inthis example, fine nickel particles are coated on the particulate layer2010, followed by injection co-molding with a fugitive-bound mixedcemented carbide and steel powder composite perform. The assembly isplaced in an elastomer mold with steel powders and a carbide particulatesurface layer as described in U.S. Pat. No. 5,967,248 (which is herebyincorporated by reference for all purposes) and densified by coldisostatic pressing to produce a final composite powder preform. Thefinal preform is then preheated to forging temperature and densified byforging, e.g., in a hot powder bed. The resulting fully densefunctionally-graded composite tool is then finish machined and heattreated.

FIG. 21 illustrates the macrostructure of such a composite road ormining pick 2100, including the cemented carbide tip 2005, theparticulate layer 2010, the undulant surface 2015, the steel shank 2105formed during cold isostatic pressing, and the densified cementedcarbide and steel powder 2110. FIG. 20 depicts the microstructure of thenon-planar interface, including the cemented carbide tip 2005, nickellayer 2005, and the densified cemented carbide and steel powder 2110.

In one particular embodiment of the present invention, a compositestructure is provided. The composite structure includes a first portioncomprising a first metallic material, a monolayer of particles extendinginto and bonded with the first portion, and a second portion comprisinga second material, the second portion bonded with the monolayer ofparticles and extending into interstices between the particles.

In another particular embodiment of the present invention, an insert fora rock bit is provided. The insert includes a substrate comprising afirst metallic material, a plurality of particles bonded with thesubstrate, and a densified portion comprising a second material, thedensified portion bonded with the plurality of particles and extendinginto interstices between the particles.

In yet another particular embodiment of the present invention, acomposite road pick is provided. The road pick includes a tip comprisinga first metallic material, a plurality of particles bonded with the tip,and a densified portion comprising a second material, the densifiedportion bonded with the plurality of particles and extending intointerstices between the particles.

In another particular embodiment of the present invention, a method forfabricating a composite structure is provided. The method includesbonding a monolayer of particles to a first portion comprising a firstmetallic material, such that the monolayer of particles extends into thefirst portion and bonding a second portion comprising a second materialto the monolayer of particles, such that the second portion extends intointerstices between the particles.

This concludes the detailed description. The particular embodimentsdisclosed above are illustrative only, as the invention may be modifiedand practiced in different but equivalent manners apparent to thoseskilled in the art having the benefit of the teachings herein.Furthermore, no limitations are intended to the details of constructionor design herein shown, other than as described in the claims below. Itis therefore evident that the particular embodiments disclosed above maybe altered or modified and all such variations are considered within thescope and spirit of the invention. Accordingly, the protection soughtherein is as set forth in the claims below.

1. A composite structure, comprising: a first portion comprising a firstmetallic material; a monolayer of particles extending into and bondedwith the first portion; and a second portion comprising a secondmaterial, the second portion bonded with the monolayer of particles andextending into interstices between the particles.
 2. A compositestructure, according to claim 1, wherein at least some of the particlesand the first portion define recesses exhibiting negative draft anglesinto which the second portion extends.
 3. A composite structure,according to claim 1, wherein the monolayer of particles is co-sinteredwith the first portion.
 4. A composite structure, according to claim 1,wherein the monolayer of particles is bonded to the first portion bymetallurgical neck bonds.
 5. A composite structure, according to claim1, wherein the monolayer of particles comprises one of the firstmetallic material, a chemical variant of the first metallic material, ametallurgical variant of the first metallic material, a metal, and ametal alloy.
 6. A composite structure, according to claim 1, wherein thefirst metallic material comprises a first cemented carbide and thesecond material comprises one of a second cemented carbide, a diamondcomposite material, a metal, and a metal alloy.
 7. A compositestructure, according to claim 1, wherein the monolayer of particlescomprises at least one of spherical particles, oblate sphericalparticles, cylindrical particles, rod-shaped particles, and irregularshaped particles.
 8. A composite structure, according to claim 1,wherein the first portion is harder than the second portion.
 9. Acomposite structure, according to claim 1, wherein the first portion issofter than the second portion.
 10. A composite structure, according toclaim 1, further comprising a second monolayer of particles extendinginto and bonded with the first portion and a third portion comprising athird material, the third portion bonded with the second monolayer ofparticles and extending into interstices between the particles of thesecond monolayer of particles.
 11. A composite structure, according toclaim 1, wherein the second portion comprises a densified powder.
 12. Acomposite structure, according to claim 1, wherein the second portioncomprises a solidified metal or metal alloy.
 13. An insert for a rockbit, comprising: a substrate comprising a first metallic material; aplurality of particles bonded with the substrate; and a densifiedportion comprising a second material, the densified portion bonded withthe plurality of particles and extending into interstices between theparticles.
 14. An insert, according to claim 13, wherein at least someof the plurality of particles and the substrate define recessesexhibiting negative draft angles into which the densified portionextends.
 15. An insert, according to claim 13, wherein the plurality ofparticles is co-sintered with the substrate.
 16. An insert, according toclaim 13, wherein the plurality of particles comprises one of the firstmetallic material, a chemical variant of the first metallic material, ametallurgical variant of the first metallic material, a metal, and ametal alloy.
 17. An insert, according to claim 13, wherein the firstmetallic material comprises a first cemented carbide and the secondmaterial comprises one of a second cemented carbide, a diamond compositematerial, a metal, and a metal alloy.
 18. An insert, according to claim13, wherein the plurality of particles comprises at least one ofspherical particles, oblate spherical particles, cylindrical particles,rod-shaped particles, and irregular shaped particles.
 19. A compositepick, comprising: a tip comprising a first metallic material; aplurality of particles bonded with the tip; and a densified portioncomprising a second material, the densified powder bonded with theplurality of particles and extending into interstices between theparticles.
 20. A composite pick, according to claim 19, wherein the tipdefines an undulant surface and the plurality of particles is bondedwith the undulant surface.
 21. A composite pick, according to claim 19,wherein at least some of the plurality of particles and the tip definerecesses exhibiting negative draft angles into which the second portionextends.
 22. A composite pick, according to claim 19, wherein theplurality of particles is co-sintered with the substrate.
 23. Acomposite pick, according to claim 19, wherein the plurality ofparticles comprises one of the first metallic material, a chemicalvariant of the first metallic material, a metallurgical variant of thefirst metallic material, a metal, and a metal alloy.
 24. A compositepick, according to claim 19, wherein the first metallic materialcomprises a first cemented carbide and the second material comprises oneof a second cemented carbide, a cemented carbide and steel mixture, ametal, and a metal alloy.
 25. A composite pick, according to claim 20,wherein the plurality of particles comprises at least one of sphericalparticles, oblate spherical particles, cylindrical particles, rod-shapedparticles, and irregular shaped particles.
 26. A method for fabricatinga composite structure, comprising: bonding a monolayer of particles to afirst portion comprising a first metallic material, such that themonolayer of particles extends into the first portion; and bonding asecond portion comprising a second material to the monolayer ofparticles, such that the second portion extends into interstices betweenthe particles.
 27. A method, according to claim 26, wherein bonding themonolayer of particles further comprises co-sintering the monolayer ofparticles with the first portion.
 28. A method, according to claim 26,wherein bonding the second portion further comprises: filling theinterstices with a powder; and pressure densifying the powder.
 29. Amethod, according to claim 26, wherein bonding the second portionfurther comprises: infiltrating the interstices with a liquid metal; andallowing the liquid metal to solidify.
 30. A method, according to claim26, further comprising extending the second portion into recessesdefined by the particles and the first portion.
 31. A method, accordingto claim 30, wherein the recesses exhibit negative draft angles.
 32. Amethod, according to claim 26, further comprising: bonding a secondmonolayer of particles to a first portion, such that the secondmonolayer of particles extends into the first portion; and bonding athird portion comprising a third material to the second monolayer ofparticles, such that the third portion extends into interstices betweenthe particles of the second monolayer of particles.